(87b) Drag Models and Their Validation: Unanswered Questions from the Past and Targeting Future Validation

Predicting accurate fluidized particle behavior with computational fluid dynamics (CFD) is potentially beneficial to industry via improving operation scaling up speed and reliability, fluidized bed operational efficiency, troubleshooting existing operations as well as exploring new equipment design, etc. Modeling the drag force, a major component of the fluid-particle momentum exchange, is essential to establishing a relevant toolbox for predicting fluidized particle behavior. Currently, a gamut of drag models exist, ranging from models that are based on the assumption of homogenous distributions of particles with each fluid grid to models that utilize sub-grid formulations to account for solids volume fractions gradients (i.e., heterogeneous particle distributions). A critical, comprehensive review of these models is presented with a focus on the parameter space relevant to development and validation. Key findings with respect to the limited range of experiments used for validating models, and the mismatch in drag model validation across different fluidization regimes are reported. Furthermore, the potential influence of neglecting, or incorrectly modeling, physical interactions between particles (e.g. cohesion, friction) are explored along with the effect of erroneously attributing all inaccuracies of the simulation to the drag model. Gaps associated with the experimental data available for model calibration and validation are discussed.